The present invention concerns mechanical high-frequency band-pass filters comprising a number of resonators formed of metallic bars (for example of stainless steel), which vibrate longitudinally in compression and extension and which are coupled together by coupling rods constituting mechanical acoustic transmission line elements and working in flexure. Such filters are used in carrier-current telephone transmission circuits, the central frequency of the transmitted band being, for example, 128 kHz and the bandwidth being 4 kHz.
The resonator bars are, in known manner, of cylindrical form with their axes parallel and situated in a common plane. They are coupled together by rectilinear rods situated substantially in this same plane and connected to at least one of the plane terminal faces of the resonators, situated in a plane perpendicular to the said axes. The inter-resonator lengths of these coupling rods (hereinafter briefly referred to as "couplers"), which work in bending, are in an appropriately calculated ratio to the propagation wavelength in the said rods for the central frequency of the operating frequency band.